1. Field of the Invention
The present invention relates to a RAID apparatus which manages the redundancy of data using a physical disk such as a magnetic disk and a logical device expansion method thereof, and more particularly to a RAID apparatus which increases the capacity of the RAID group or adds redundancy to the RAID group, and the logical device expansion method thereof.
2. Description of the Related Art
In a storage device using such storage medium as a magnetic disk, magneto-optical disk and optical disk, the storage medium is actually accessed by the request of a data processing apparatus. When the data processing apparatus handles large capacity data, a storage system included a plurality of storage devices and a control apparatus is used.
In such a storage system, a redundant configuration is used to improve the reliability of the stored data and the reliability of the device. For the redundant configuration, the disk device normally uses a multiplex configuration of disks called a RAID (Redundant Array of Inexpensive (or Independent) Disks). As RAID functions, RAID 0, RAID 1, RAID 0+1, RAID 2, RAID 3, RAID 4 and RAID 5 are known.
In such a RAID configuration, the RAID level is fixed in the system. However, if the redundancy is increased, the reliability improves but the performance drops, and if the redundancy is decreased, the reliability drops but the performance improves. The redundancy is determined by the system configuration of the user, but there is a demand that the user wants to change the redundancy after installing the system. The redundancy can be easily changed if the system is shutdown.
But when an online system is constructed, it is desirable that the redundancy can be changed in an active status without shutting down the system. Prior proposed method is to change the redundancy in an active status by decreasing or increasing the parity blocks (e.g. Japanese Patent Application Laid-Open No. H7-306758 (see FIG. 2, FIG. 7, FIG. 8).
According to this proposal, in the configuration of RAID 5, data is read from a physical disk group to a cache memory, redundancy is decreased from 2 parities or 1 parity to 1 parity or 0 parity, or redundancy is increased from 0 parity or 1 parity to 1 parity or 2 parities, and the data is written from the cache memory to the physical disk group.
If an I/O request is received from the host during this redundancy conversion processing, the redundancy conversion processing is interrupted and it is judged whether the I/O request is for the area where the redundancy change has completed or for the area where the redundancy has not been changed, and then the I/O request is executed. In the case of redundancy reduction, the actual disks must be decreased, and in the case of redundancy increase, the actual disks must be increased.
In prior art, however, the redundancy can be changed in an active status, but the change of various RAID levels cannot be supported since this is a technology to simply decrease or increase the number of parity blocks, where the range of change of the redundancy is limited.
Further, it is difficult that the demand for increasing the capacity of the RAID group without changing the RAID level in an active status be implemented.